Background.
Disposal of wastes is one of the largest problems facing the world today. Disposal of hazardous wastes, in particular, is a great problem, because of the necessity to provide safe isolation of the hazards from the environment. A preferable method of hazardous waste disposal is pressure injection into impermeable geologic formations, using hydraulic fracture processes. Waste must be injected below or contained within impermeable layers which contain and seal the hazardous materials from critical zones, reservoirs, aquifers and sources of useful waters.
There is a problem with fracture disposal, however, in knowing where the fractures occur, their growth and propagation in unknown directions, and the possibility that hydraulic fractures and wastes injected into them might migrate in unknown directions and pollute sources of drinking water and other critical geologic zones. For that reason, underground injecting of hazardous wastes without an approved EPA exemption is prohibited. Passive Seismic Imaging (PSI) is an emerging technology which can be used for real time scientific verification of geologic containment of hazardous wastes injected into subterranean hydraulic fractures. Passive Seismic Imaging of hydraulic fractures used for the disposal of hazardous waste as disclosed in this invention will provide real time location, visualization and verification of containment which may meet EPA demonstration requirements for geologic containment of the wastes.
Moreover, in hydraulic fracturing to stimulate production from low permeability oil and gas reservoirs, improved controls are urgently needed. As the interwell spacing in a hydraulically fractured reservoir decreases through further field development, there is an increasing need for precise information concerning the geometry, dimensions, and orientation of the induced fractures, in order to design the well pattern necessary for efficient drainage. Passive Seismic Imaging, including automatic data acquisition, data compression, processing, display and visualization as disclosed herein provides a technology which satisfies this need.
Previous technology. During the 1930's and 40's, it was common in oil and gas exploration to drill into subterranean formations that contained oil and gas but that produced at uneconomically low flow rates. A method for increasing such low flow rates was developed by J. B. Clark in 1948 . The method, called "fracturing", was based on the observation that pressure applied at the wellhead to an incompressible fluid would be transmitted downhole to the exposed formation, which would part under the transmitted stress.
U.S. Pat. Nos. 3,108,439 to REYNOLDS et al; 3,262,274 to NELSON, Jr.; 3,292,693 to HILL et al; 3,331,206 to OSBORNE; 3,335,798 to QUERIO et al; 3,374,633 to BRANDT; 3,513,100 to STOGNER; 3,852,967 to STEWART et al; 3,576,513 to LINDERHOFFER et al; 4,787,452 to JENNINGS, JR.; 4,828,030 to JENNINGS, JR.; 4,906,135 to BRASSOW et al; 4,942,929 to MALACHOSKY et al; 5,108,226 to JENNINGS; 5,109,933 to JACKSON; 5,129,469 to JACKSON; 5,133,624 to CAHILL; and 5,191,157 to CROCKER disclose various waste disposal methods involving drilling into suitable subterranean formations and injecting various materials for permanent storage, e.g., radioactive liquids or slurries, waste solids or sludges, or other liquids or gasses, into underground formations. As described in the STOGNER patent for example, a mixture of sharply angular solid waste particles and an aqueous cement are used to fracture and prop open an underground formation. Any incompressible fluid, like cement, can be used as a fracturing inducing fluid, but as described in CAHILL, not all fracture inducing fluids are suitable for permanent waste disposal.
REYNOLDS and NELSON disclose methods of disposing of radioactive wastes. HILL discloses disposal of toxic fluids. BRASSOW, CAHILL and CROCKER disclose disposal of hazardous wastes. Others listed above, using generic terms such as wastes, solid particles, finely ground solids, waste materials, pumpable wastes, and the like, may include hazardous wastes as well. In particular, REYNOLDS, CAHILL and CROCKER disclose disposal into induced hydraulic fractures.
U.S. Pat. No. 3,739,871 to BAILEY teaches the mapping of earth fractures induced by hydrafracturing for gas and oil production; and while BAILEY uses pressure gauges and seismometers in his process, it is not applied to location of hazardous wastes, and is not a real time location and display.
U.S. Pat. No. 4,802,144 to HOLZHAUSEN, ET AL is a method for hydraulic fracture analysis. U.S. Pat. No. 5,010,527 to MAHRER is a method for determining the depth of a hydraulic fracture zone in the earth.
But none teaches a method for real time, automatic calculation, computer imaging, visualization and display of hydraulic fracture location, dimensions and geometry for interactive management of fracturization and for verifying the location and containment of wastes that have been so disposed.